Warming ocean water undercuts Antarctic ice shelves

March 14, 2016

"Upside-down rivers" of warm ocean water threaten the stability of floating ice shelves in Antarctica, according to a new study led by researchers at the University of Colorado Boulder's National Snow and Ice Data Center published today in Nature Geoscience. The study highlights how parts of Antarctica's ice sheet may be weakening due to contact with warm ocean water.

"We found that warm ocean water is carving these 'upside-down rivers,' or basal channels, into the undersides of ice shelves all around the Antarctic continent. In at least some cases these channels weaken the ice shelves, making them more vulnerable to disintegration," said Karen Alley, a Ph.D. student in CU-Boulder's Department of Geological Sciences and lead author of an analysis published today in Nature Geoscience.

Ice shelves are thick floating plates of ice that have flowed off the Antarctic continent and spread out onto the ocean. As ice shelves flow out to sea, they push against islands, peninsulas, and bedrock bumps known as "pinning points." Contact with these features slows the flow of grounded ice off the continent. While ice shelves take thousands of years to grow, previous work has shown that they can disintegrate in a matter of weeks. If more ice shelves disintegrate in the future, loss of contact with pinning points will allow ice to flow more rapidly into the ocean, increasing the rate of sea level rise.

"Ice shelves are really vulnerable parts of the ice sheet, because climate change hits them from above and below," said NSIDC scientist and study co-author Ted Scambos. "They are really important in braking the ice flow to the ocean."

The features form as buoyant plumes of warm and fresh water rise and flow along the underside of an ice shelf, carving channels much like upside-down rivers. The channels can be tens of miles long, and up to 800 feet "deep."

When a channel is carved into the base of an ice shelf, the top of the ice shelf sags, leaving a visible depression, or "wrinkle", in the relatively smooth ice surface. Alley and her colleagues mapped the locations of these wrinkles all around the Antarctic continent using satellite imagery, as well as radar data that images the channels through the ice, mapping the shape of the ice-ocean boundary.

The team also used satellite laser altimetry, which measures the height of an ice shelf surface with high accuracy, to document how quickly some of the channels were growing. The data show that growing channels on the rapidly melting Getz Ice Shelf in West Antarctica can bore into the ice shelf base at rates of approximately 10 meters (33 feet) each year.

The mapping shows that basal channels have a tendency to form along the edges of islands and peninsulas, which are already weak areas on ice shelves. The team observed two locations where ice shelves are fracturing along basal channels, clear evidence that basal channel presence can weaken ice shelves to the point of breaking in vulnerable areas.

Ice shelves are thick floating plates of ice that have flowed off the continent and out onto the ocean. As ice shelves flow out to sea, they push against islands, peninsulas, and bedrock bumps known as "pinning points". Contact with these features slows the ice flowing off the continent. If ice shelves disintegrate in the future, loss of contact with pinning points will allow ice to flow more rapidly into the ocean, increasing rates of sea level rise.

While no ice shelves have completely disintegrated due to carving by basal channels, the study points to the need for more observation and study of the features, said co-author... "It's feasible that increasing ocean temperatures around Antarctica could continue to erode ice shelves from below."

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21 comments

How do we know you're not lying, like the rest of the "climate scientists"?

"Two decades ago, the question was: Is global warming alarmism simply false or is it fraudulent?

Now, after the Mann hockey stick fiasco, "Mike's Nature trick", "Hide the Decline", the fabricated aerosol data used to false-hindcast the warming alarmists' climate models, the Climategate emails, and the many false "adjustments" of the surface temperature data record, there is no question:

Global warming alarmism is clearly fraudulent – in financial terms, it is one of the greatest frauds of all time." -- Allan MacRae

You know, I did a brief search for the quote you provided, and interestingly, the only place it seemed to appear is AS A COPY-PASTED COMMENT in wattsupwiththat, which is a climate denial website run by somebody who has no business acting like he's an expert in climatology.

Maybe you should look again. In particular, I notice very little correlation between positions of subglacial channels and the volcanoes, though, admittedly, I am eyeballing it. If you look at the map you provided, the volcanoes all occur around the coastline in quadrants II and III, whereas the channels happen all over the place. Now, I am no expert on spatial correlation, but off the top of my head, one way of getting at least a sense of whether your hypothesis might be correct is to perform the following procedure:(to be continued)

1) split your map into cells2) For each cell, compute two functions Dv, and Dc. Dv is the average distance of the cell's center to the nearest volcano, and Dc is the average distance from the cell's center to the nearest channel.3) Assuming each cell is marked Xij, where (i,j) is a coordinate, you can now treat Dv and Dc like variables on Xij. Compute the correlation between Dv and Dc.

If you get a significant correlation, and assuming nobody can offer a better strategy for determining how well they are correlated that nullifies the result of your calculation, then your hypothesis is worth exploring more.

Or, we could do it your way, and eyeball it, and then assume that that should be given equal weight to the experts who understand the subject WAAAAAAY better than you, because if we know anything about scientific results, its that they are obtained by eyeballing data. That's how it works, right?

I was going to finish my comments there, but I thought this was a good opportunity to ask whether the researchers actually took heating from seismic activity into account.

Again, we could do things your way, and assume they are incompetent buffoons (I call it the Dunning Kruger method of science), or, we could do things THE RIGHT way, and find out sufficient information about their methods before showing your obvious bias by jumping to conclusions.

Very telling is the fact that they choose to be vague about the true source of the heat.

By antigoracle's argument, there are volcanoes in the world and I am in the world, therefore volcanoes are CLEARLY responsible for why I'm warm right now. This is like people blaming GM mosquitoes for Zika because they're both in Brazil and ignoring the fact that the outbreak was hundreds of kilometres away. Brazil and Antarctica - big places. Maybe this is the natural human heuristic that causes Americans to ask Australians if they know another Australian even though they live 3000km away.

By antigoracle's argument, there are volcanoes in the world and I am in the world, therefore Maybe this is the natural human heuristic that causes Americans to ask Australians if they know another Australian even though they live 3000km away.

happens to me all the time when I say I'm from Chicago (area)Oh. And the air-gangster/tommygun thing, too...

....Or, we could do it your way, and eyeball it, and then assume that that should be given equal weight to the experts who understand the subject WAAAAAAY better than you.....

His map of volcanoes doesn't indicate evidence that East Antarctica is split by an active rift zone. It's location is marked by the series of giant lakes deeply buried under ice. This pattern of large lakes is also seen in Africa.

While I agree with you actually. I'd hesitate to base so much on the limited information we have on volcanoes that have been verified beyond a doubt as being on that continent.

Science deals in proof as you know, and it's hard to get proof about what's happening 2+ miles under ice. As a result a lot of indicators that there might be widespread volcanic activity is ignored until researchers are able to get enough proof to meet the fact threshold.

While I agree with you actually. I'd hesitate to base so much on the limited information we have on volcanoes that have been verified beyond a doubt as being on that continent.

Science deals in proof as you know, and it's hard to get proof about what's happening 2+ miles under ice. As a result a lot of indicators that there might be widespread volcanic activity is ignored until researchers are able to get enough proof to meet the fact threshold.

Jonseer,

I didn't rank this comment, because it is unclear to me what is its intent. We can all agree that vulcanism contributes to the heat flux subglacially in Antarctica, and all agree that vulcanism is present in both EA and WA.

The common misperception is to equate vulcanism with roiling pools of lava, when, in fact --and especially so in this case, the flux is represented almost entirely via the odd hot spring(at very shallow depth), steam vent or fissure.

In both EA and WA, the weight of the ice itself is sufficient to suppress vulcanism almost entirely, with the exception of surface and very near surface volcanoes.

Otherwise, the earth itself is quite an effective insulator, capable of retaining virtually all of the subsurface heat due to vulcanism.

For this reason, geothermally derived glacial melting, while it does occur, can only be said to be a minimal contributor to the over all heat flux, continent wide.

This means that the real cause of all this melting is something else entirely.

And there is only one other process capable of generating this much heat flux.

Perhaps you'd like to guess, why gloBull warming is so concentrated in the West Antarctic compared to the rest of it.

Umm, because it's got more ice shelves?

Duh.

The utter ignorance of the Chicken Little idiot has lost all amusement for me, the only thing left is my pity. Pity that they relish displaying their stupidity. Imagine the conclusion, more ice shelves is the reason for more global warming. I would draw your attention to the following link, but alas it would be an exercise in futility with you ignoramuses.http://earthobser...?id=6502